They seem to be parsing the structure rather than just gluing strings, kudos for that!

However, the tricky case they've run into:

     <template name="hello">
       {{#if bold}}
         <b>Hello {{name}}!</b>
       {{else}}
         Hello {{name}}!
       {{/if}}
     </template>     

has been solved in TAL:

    <template name="hello">  
       <b tal:omit-tag="not:bold">Hello {{name}}!</b>   
    </template>